Transcutaneous medical device dressings and method of use

ABSTRACT

A transcutaneous device dressing and method for its use with a transcutaneous medical device, such as an intravascular catheter, which punctures the skin of a patient and which has a portion of the medical device protruding from the skin which can lead to infection. The dressing includes a top and a bottom dressing, both being formed from a flexible material and having upper and lower surfaces, with the lower surface being the skin facing surface in use. The bottom dressing has a slit formed therein extending from one edge inwardly to a termination point within the confines of the bottom dressing. An anti-microbial material is provided without the use of adhesives at the upper and lower surfaces of the bottom dressing, and at least at the lower surface of the top dressing. In use, the bottom dressing is placed next to the skin, the slit allowing the bottom dressing to surround the puncture site such that the lower surface of the bottom dressing is in contact with the skin while the upper surface of the bottom dressing is in contact with a portion of the medical device protruding from the skin. The top dressing is placed above the puncture site such that its lower surface is in contact with a portion of the medical device protruding from the skin. In this way, there is exposure of the portion of the medical device protruding from the skin to the anti-microbial activity of the anti-microbial material.

FIELD OF THE INVENTION

The invention relates to transcutaneous medical device dressings, andprocesses for their production and use, for controlling infections.

BACKGROUND OF THE INVENTION

Transcutaneous medical devices are catheters, pins, implants and thelike which pass through the skin and are indwelling for someconsiderable time. Exemplary of transcutaneous medical devices arecentral venous catheters, peripheral venous catheters, Swan-Gauzpulmonary catheters, central nervous system implants (ex. externalventricular drainage and ventricular reservoirs), peritoneal dialysiscatheters, such as for continuous ambulatory peritoneal dialysis andcontinuous cyclic peritoneal dialysis, hemodialysis catheters,transvenous pacemaker leads and temporary orthopedic pins. All of thesetranscutaneous medical devices, when in place, have a portion of thedevice which is external, that is which is left protruding from theskin, and which can be the the cause of infection.

The risk or acquiring infections from transcutaneous infections is veryhigh. For instance, the risk of acquiring catheter-related bloodstreaminfection ranges from 0.9 to 8%. This nosocomial bloodstream infectionscause a case fatality of more than 20%, and account for an increase ofthousands of dollars in hospital costs per infection, or tens ofthousands of dollars per survivor in ICU needing an extra week ofhospital stay. As for peritoneal dialysis, a very experienced centertoday still has a peritonitis rate of one episode per 15 to 25 patientmonths. The major sources of bacteria in these infections are fromsurrounding skin.

To prevent infections associated with transcutaneous medical devicesantiseptic preparation of insertion sites, including the initialapplication of topical anti-microbial solutions such as alcohol oriodine to the insertion sites is known. A further topical ointment afterinsertion of the device, such as an ointment containing neomycin,polymyxin and bactracin, has been shown to prevent cathetercolonization/infection, but it may increase the risk or fungalinfection. Ointments are also inconvenient, requiring multiplereplacements. There have also been attempts to attach a cuff to thecatheters, with an anti-microbial agent impregnated in the cuff. Effortsto coat the catheters with anti-microbial agents are known. However,none of these efforts has been completely successful in clinical trials.Presently, the most common catheter dressing used in hospitals comprisessterile gauze or polyurethane film, which have limited infection controlproperties.

Recent efforts to replace gauze with a transparent film dressing toallow a visual check on the insertion site is known, see for instanceU.S. Pat. No. 5,372,589, issued Dec. 13, 1994 to Davis. Noanti-microbial control is taught with such a dressing. Johnson & JohnsonMedical Inc. markets a product under the trade mark BIOPATCH, which is achlorhexidine gluconate-impregnated catheter patch. An Iodophortransparent dressing has also been suggested. However, to date, nocompletely effective anti-microbial device for use with transcutaneousmedical devices is known.

A securement devices is taught for securing a intravenous device to thebody in U.S. Pat. No. 3,918,446, issued Nov. 11, 1975 to Buttaravoli.The device has an upper and a lower pad, between which the intravenousdevice is fixed. Since the function of the device is to secure thedevice to the body, there is a teaching to provide an adhesive materialto the bottom of lower pad, and to the bottom of the top pad. There is amention of providing the adhesive with an antibacterial agent. Thisdevice has the disadvantage of using adhesives with the antibacterialagent, which limits the effectiveness and long lasting ability of theantibacterial agent. Furthermore, the adhesive can be irritating next tothe skin, cause skin damage and patient discomfort on removal, andinhibits the removal or changing of the device. Furthermore, manyadhesives act as moisture barriers, which can limit the effectiveness ofthe antibacterial agent. Finally, the device of this patent teachesincluding a slit in the bottom pad of the dressing, which lies below theintravenous needle or catheter when the device is in place, allowing theintravenous device to remain in contact with the skin, and thereforelimiting the infection control of the device.

SUMMARY OF THE INVENTION

In one broad aspect, the invention provides a transcutaneous devicedressing for use with a transcutaneous medical device which haspunctured the skin of a patient and which has a portion of the medicaldevice protruding from the skin, comprising:

a top and a bottom dressing, both being formed from a flexible materialand having upper and lower surfaces, with the lower surface being skinfacing in use;

the bottom dressing having a slit formed therein extending from one edgeinwardly to a termination point within the confines of the bottomdressing;

an anti-microbial material provided without adhesives at the upper andlower surfaces of the bottom dressing, and at least at the lower surfaceof the top dressing:

whereby, in use, the bottom dressing is placed next to the skin, theslit allowing the bottom dressing to surround the puncture site suchthat the lower surface of the bottom dressing is in contact with theskin and the upper surface of the bottom dressing is in contact with aportion of the medical device protruding from the skin, and the topdressing is placed above the puncture site such that its lower surfaceis in contact with a portion of the medical device protruding from theskin, thereby exposing a portion of the medical device protruding fromthe skin from above and below to the anti-microbial activity of theanti-microbial material.

In another broad aspect, the invention provides a method of dressing thepuncture site of a transcutaneous medical device to limit infection bymicroorganisms from the surrounding skin and the portion of the medicaldevice that protrudes from the skin of a patient, comprising:

providing a transcutaneous device dressing, comprising:

a top and a bottom dressing, both being formed from a flexible materialand having upper and lower surfaces, the lower surfaces being skinfacing when the dressing is in use;

the bottom dressing having a slit formed therein extending from one edgeinwardly to a termination point within the confines of the bottomdressing; and

an anti-microbial material provided without the use of adhesives at theupper and lower surfaces of the bottom dressing, and at least at thelower surface of the top dressing;

sliding the bottom dressing in place next to the skin using the slit toallow the bottom dressing to surround the puncture site at thetermination point such that the lower surface of the bottom dressing isin contact with the skin surrounding the puncture site while the uppersurface of the bottom dressing is in contact with a portion of themedical device protruding from the skin;

applying the top dressing above bottom dressing such that its lowersurface is in contact with a portion of the medical device protrudingfrom the skin;

depending on the anti-microbial material, applying a water or alcoholbased electrolyte to the top and bottom dressings to release theanti-microbial agent; and

fixing the top and bottom dressings to the skin, preferably with anocclusive or semi-occlusive layer such as an adhesive film.

The transcutaneous device dressing of this invention has the advantageof ease of placement and been demonstrated to be much more effectivethan disc type dressings which are laid flat under the transcutaneousdevice, which have only a limited portion, generally only the thicknessof the dressing (less than 3 mm), in contact with the portion of themedical device which protrudes from the skin.

Preferably, the dressing of this invention is formed such that the topand bottom dressings are joined along a fold line, that is they areformed from a unitary dressing which is folded over in use. The slit ispreferably formed from the edge of the bottom dressing which is parallelto the fold. The dressing is preferably formed from multilayered,laminated dressing materials. The anti-microbial material is preferablya thin film of an anti-microbial metal, most preferably formed withatomic disorder so as to create an effective anti-microbial effect, andto create an interference colour so as to provide an indicator, asdescribed in WO98/41095, published Sep. 24, 1998, and naming inventorsR. E. Burrell and R. J. Precht.

The dressing of this invention has application to transcutaneous medicaldevices such as listed above, made from a wide variety of materials, forexample metals, including steel, aluminum and its alloys, latex, nylon,silicone, polyester, polyurethane, and other plastics and rubbers. Suchdevices are generally made of a bioinert or Biocompatible material. Thedevice may take a variety of shapes including rod or tube shapes, hollowor solid, and may be rigid or flexible, factors dictated by its intendedutility.

As used herein and in the claims, the terms and phrases set out belowhave the meanings which follow.

“Metal” or “metals” includes one or more metals whether in the form ofsubstantially pure metals, alloys or compounds such as oxides, nitrides,borides, sulphides, halides or hydrides.

“Anti-microbial metals” are metals whose ions have an anti-microbialeffect. Preferably, the metal will also be biocompatible. Preferredanti-microbial metals include Ag, Au, Pt, Pd, Ir (i.e. the noblemetals), Sn, Cu, Sb, Bi and Zn, with Ag being most preferred.

“Biocompatible” means non-toxic for the intended utility. Thus, forhuman utility, biocompatible means non-toxic to humans or human tissues.

“Anti-microbial effect” means that atoms, ions, molecules or clusters ofthe anti-microbial metal (hereinafter “species” of the anti-microbialmetal) are released into the alcohol or electrolyte which the materialcontacts in concentrations sufficient to inhibit bacterial (or othermicrobial) growth in the vicinity of the material. The most commonmethod of measuring anti-microbial effect is by measuring the zone ofinhibition (ZOI) created when the material is placed on a bacteriallawn. A relatively small or no ZOI (ex. less than 1 mm) indicates a nonuseful anti-microbial effect, while a larger ZOI (ex. greater than 5 mm)indicates a highly useful anti-microbial effect. One procedure for a ZOItest is set out in the Examples which follow.

“Sustained release” or “sustainable basis” are used to define release ofatoms, molecules, ions or clusters of an anti-microbial metal thatcontinues over time measured in hours or days, and thus distinguishesrelease of such metal species from the bulk metal, which release suchspecies at a rate and concentration which is too low to achieve ananti-microbial effect, and from highly soluble salts of anti-microbialmetals such as silver nitrate, which releases silver ions virtuallyinstantly, but not continuously, in contact with an alcohol orelectrolyte.

“Atomic disorder” includes high concentrations of: point defects in acrystal lattice, vacancies, line defects such as dislocations,interstitial atoms, amorphous regions, gain and sub grain boundaries andthe like relative to its normal ordered crystalline state. Atomicdisorder leads to irregularities in surface topography andinhomogeneities in the structure on a nanometer scale.

“Normal ordered crystalline state” means the crystallinity normallyfound in bulk metal materials, alloys or compounds formed as cast,wrought or plated metal products. Such materials contain only lowconcentrations of such atomic defects as vacancies, grain boundaries anddislocations.

“Diffusion”, when used to describe conditions which limit diffusion inprocesses to create and retain atomic disorder, i.e. which freeze-inatomic disorder, means diffusion of atoms and/or molecules on thesurface or in the matrix of the material being formed.

“Alcohol or water-based electrolyte” is meant to include any alcohol orwater-based electrolyte that the anti-microbial materials of the presentinvention might contact in order to activate (i.e. cause the release ofspecies of the anti-microbial metal) into same. The term is meant toinclude alcohols, water, gels, fluids, solvents, and tissues containingwater, including body fluids (for example blood, urine or saliva), andbody tissue (for example skin, muscle or bone).

“Colour change” is meant to include changes of intensity of light undermonochromatic light as well as changes of hue from white lightcontaining more than one wavelength.

An “interference colour” is produced when light impinges on two or morepartly reflective surfaces separated by a distance which bears the rightrelationship to the wavelength of the light to be removed by destructiveinterference.

“Partly reflective” when used to describe the base or top layermaterials, means that the material has a surface which reflects aportion of incident light, but which also transmits a portion of theincident light. Reflection occurs when a ray of incoming lightencounters a boundary or interface characterized by a change inrefractive index between two media. For the top layer of theanti-microbial materials of this invention, that interface is with air.For the basic layer, the interface is with the top layer. Thereflectance of the base and top layers is balanced so as to generate aninterference colour.

“Partly light transmissive” when used to describe a thin film of the toplayer material means that the thin film is capable of transmitting atleast a portion of incident visible light through the thin film.

“Detectable” when used to describe a colour change means an observableshift in the dominant wavelength of the reflected light, whether thechange is detected by instrument, such as a spectrophotometer, or by thehuman eye. The dominant wavelength is the wavelength responsible for thecolour being observed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional figure of a three layer transcutaneousdevice dressing in accordance with the present invention;

FIG. 2 is a schematic perspective view of a three layer transcutaneousdevice dressing folded along a central line to form top and bottomdressings and showing the slit for placement around the transcutaneousmedical device;

FIG. 3 is a schematic sectional view of the folded transcutaneous devicedressing in place with a catheter penetrating the skin of a patient;

FIG. 4 is a plan view of the transcutaneous device dressing of thisinvention, showing the slit in the bottom dressing;

FIG. 5 is a plan view of the transcutaneous device dressing slid inplace with a catheter, such that the bottom dressing is in contact witha portion of the catheter protruding from the skin; and

FIG. 6 is a plan view of transcutaneous device dressing folded such thatthe top dressing is in contact with a portion of the catheter protrudingfrom the skin.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Transcutaneous Device Dressing

The dressing in accordance with the invention includes at least one, andpreferably at least two or three layers of medical dressing materials,laminated together by known means such as low temperature thermalfusing, stitching or, most preferably, ultrasonic welding. A three layerdressing in accordance with the invention is shown generally at 10 inFIG. 1 to include a first layer 12, which will be skin facing in use, asecond layer 14, which preferably forms an absorbent core, and a thirdlayer 16. The layers 12, 14 and 16 are shown to be laminated together byultrasonic welds 18 at intermittent locations across the dressing 10.

FIG. 2 shows the dressing 10 to comprise a top dressing 20 and a bottomdressing 22 formed from the three layers 12, 14 and 16. In FIG. 2, thetop and bottom dressings 20, 22 are joined along a fold line 24, beingformed from a unitary dressing 10. However, in accordance with thisinvention, the top and bottom dressings 20, 22 may be formed fromseparately, from same or different medical dressing materials. If thetop and bottom dressings 20, 22 are provided separately, the topdressing 20 may include an occlusive or semi-occlusive layer such as anadhesive film (not shown) in order to secure the dressing 10 in place,and retain moisture for activation of the anti-microbial material. Aslit 26 is formed in the bottom dressing 22, preferably extending fromthe edge of the bottom dressing 22 which is parallel to the fold line24, and terminating at a termination point 28 which is preferably aboutthe center point of the bottom dressing 22.

The dressing 10 is shown in place against the skin 30 of a patient inFIG. 3, with a catheter 32 protruding from the skin 30 at a penetrationsite 34. The dressing is held in place against the skin with anocclusive or semi-occlusive layer 36, such as adhesive tape orpolyurethane film. The dressing is sized to cover a significant portionof the catheter 32 that protrudes from the skin 30, and not just theimmediate skin area surrounding the penetration site. This aids inlimiting infection, since bacteria arc prevented from migrating alongthe catheter 32. A minimum dressing size will preferably provide atleast 5 mm coverage of the protruding catheter 32, more preferably 1-5cm coverage.

Depending on the size of the transcutaneous medical device, thetermination point 28 of the slit 26, may include additional cuts,preferably a cross-cut, or a penetrating hole (not shown), to allow themedical device to fit through the dressing, while still maintaining theportions around the termination point in close contact with both theskin and protruding section of the medical device.

FIGS. 4, 5 and 6 demonstrate placement of the dressing 10 around acatheter 32, with the bottom dressing 22 sliding under the catheter 32such that the lower surface 36 (see FIG. 2) of the bottom dressing 22contacts the patient's skin (not shown), while the upper surface 38 ofthe bottom dressing 22 contacts the catheter 32 protruding from theskin. Once the top dressing 20 is applied, by folding it over the bottomdressing 22, the lower surface 40 (see FIG. 2) of the top dressing 20 isin contact with the catheter 32 protruding from the skin. The uppersurface 42 of the top dressing 20 is then covered with the occlusive orsemi-occlusive layer 36, as shown in FIG. 3. As shown in FIGS. 4 and 5,when the dressing 10 is formed from a unitary dressing, the lowersurface 40 of the top dressing 20 and the upper surface 40 of the bottomdressing 22, are one and the same layer, represented as layer 16 in FIG.1.

The lower and upper surfaces 38 and 40 of the bottom dressing 22, and atleast the lower surface 42 of the top dressing 20 are provided with ananti-microbial material in order to limit infection. Anti-microbialmaterials for use with medical dressing materials are well known in theart. The anti-microbial material may be impregnated in one or more ofthe layers of the dressing 10, but will more preferably be provided as athin film of an anti-microbial metal on those surfaces of the top andbottom dressings 20, 22 which will be skin or catheter facing once thedressing is in place. Alternatively, the anti-microbial material may bean antibiotic composition or a composition formed from an anti-microbialmetal, as are well known in the art.

The preferred and alternate compositions of the layers 12, 14 and 16,together with the preferred anti-microbial metal coatings are set out infurther detail below.

Dressing Materials

The first layer 12 of the dressing 10 is formed of a perforated,preferably non-adherent material which allows for fluids to penetrate ordiffuse there through in either or both directions. The perforatedmaterial may be formed of a woven or non-woven, non-woven beingpreferred, fabric such as cotton, gauze, a polymeric net or mesh such aspolyethylene, nylon, polypropylene or polyester, an elastomer such aspolyurethane or polybutadiene elastomers, or a foam such as open cellpolyurethane foam. Exemplary perforated, non-adherent materials usefulfor the dressing include non-woven meshes such as DELNET™ P530, which isa non-woven veil formed of high density polyethylene using extrusion,embossing and orientation processes, produced by Applied ExtrusionTechnologies, Inc. Of Middletown, Del., USA. This same product isavailable as Exu-Dry CONFORMANT 2™ Wound Veil, from Frass SurvivalSystems, Inc., Bronx, N.Y., USA as a subset of that company's WoundDressing Roll (Non-Adherent) products. Other useful non-woven meshesinclude CARELLE™ or NYLON 90™,available from Carolina Formed FabricsCorp., N-TERFACE™, available from Winfield Laboratories, Inc., ofRichardson, Tex., USA. Exemplary woven meshes may be formed fromfibreglass or acetate, or cotton gauze. An exemplary hydrophilicpolyurethane foam is HYPOL™, available from W. R. Grace & Co., New York,N.Y., USA.

For ease of ultrasonic welding for lamination, at least one of the firstand second layers 12, 14 is preferably formed from a polymeric materialwhich is amenable to ultrasonic welding, that is which will melt on theapplication of localized heat and then fuse the layers together oncooling.

The second, absorbent layer 14 is formed from an absorbent material forholding sufficient moisture next to the skin in order to activate theanti-microbial metal coating, that is to cause release of ions,molecules, atoms or clusters of the anti-microbial metal in order tocause an anti-microbial effect. Preferably, the absorbent material is anabsorbent needle punched non-woven rayon/polyester core such as SONTARA™8411, a 70/30 rayon/polyester blend commercially available from DupontCanada, Mississauga, Ontario, Canada. This product is sold by NationalPatent Medical as an American White Cross sterile gauze pad. However,other suitable absorbent materials include woven or non-woven materials,non-woven being preferred made from fibers such as rayon, polyester,rayon/polyester, polyester/cotton, cotton and cellulosic fibers.Exemplary are creped cellulose wadding, an air felt of air laid pulpfibers, cotton, gauze, and other well known absorbent materials suitablefor medical dressings.

The third layer 16 of the dressing 10 is preferably formed ofperforated, non-adherent material such as used in the first layer 12.This allows moisture penetration as sterile water and the like are addedin order to activate the anti-microbial metal coating.

Additional layers (not shown) may be included between or above thefirst, second and third layers 12, 24, 16, as is well known in medical.Thus the use of the terms first, second and third layer, as used hereinand in the claims is not meant to exclude such additional layers.

The layers 12, 14, and 16 laminated together at intermittent spacedlocations across the dressing 10 by ultrasonic welds 18. Ultrasonicwelding is a known technique in the quilting art, and thus will not bediscussed at length. Briefly, heat (generated ultrasonically) andpressure are applied to either side of the dressing 10 at localizedspots through an ultrasonic horn so as to cause melting of at least oneof the plastic materials in the first and second layers 12, 14, and thesubsequent bonding together of the layers on cooling. The welds appearat localized circular spots and are preferably less than 0.5 cm indiameter. If the third layer 16 is present, the ultrasonic welding canbe performed from either side of the dressing, and will bind all threelayers 12, 14 and 16 together.

The use of ultrasonic welding of the layers at spaced locations has theadvantage of retaining the absorbent and moisture penetration propertiesof the layers 12, 14, while retaining the conforming properties of thedressing. Edge seams, stitching and adhesives have the disadvantage ofinterfering with one or more of these desirable properties of thedressings. Furthermore, by spacing the welds 18 at intermittentlocations across the dressing, the dressing 10 may be cut to smallersizes, as needed, without causing delamination. Preferred spacings ofabout 2.5 cm between welds allows the dressing to be cut down to about2.5 cm sizes, while maintaining at least one weld to hold the laminatedlayers together.

Anti-Microbial Coating

The dressing 10 of this invention preferably includes an anti-microbialcoating formed from an anti-microbial metal. The coating is applied toone or more of the layers 12, 14, 16, but is most preferably applied atleast to the first and third layers 12 and 16, so as to provide theanti-microbial effect both against the skin and against thetranscutaneous medical device held between the top and bottom dressings20, 22.

The coating is most preferably formed with atomic disorder in accordancewith the procedures set out above and as described in U.S. Pat. No.5,454,886, and WO98/41095, both to Burrell et al. Most preferably, thecoating is formed as a multilayer anti-microbial coating having a topand a base layer, as set below, to produce an interference colour. Inthis way, the coating provides not only an anti-microbial effect tolimit infection, but also acts as an indicator of activation of thedressing. As the top layer of the coating is activated with an alcoholor water-based electrolyte, such as sterile water or ethanol, even minordissolution of the anti-microbial metal results in a detectable colourchange, indicating that an anti-microbial effect is being provided. Ifthere is no colour change, additional moisture might be provided to thedressing by adding water, until a colour change is detected. Onceactivated, the dressing should be maintained in a moist condition by theaddition of sterile water if necessary.

Sterilization

Dressings 10 with anti-microbial coatings of an anti-microbial metalformed with atomic disorder are preferably sterilized without applyingexcessive thermal energy, which can anneal out the atomic disorder,thereby reducing or eliminating a useful anti-microbial effect. Gammaradiation is preferred for sterilizing such dressings, as discussed inU.S. Pat. No. 5,454,886.

It should be appreciated that the use of ultrasonic welding to laminatethe layers of dressings with anti-microbial coatings formed fromanti-microbial metals with atomic disorder is advantageous since itachieves bonding in localized spots and avoids applying heat to anysignificant portion of the dressing, thereby avoiding any significantreduction in the anti-microbial effect through annealing out of atomicdisorder.

The sterilized dressings should be sealed in packaging which excludeslight penetration to avoid additional oxidation of the anti-microbialcoating. Polyester peelable pouches are preferred. The shelf life ofanti-microbial dressings thus sealed is over one year.

Directions for Use of Dressings with Transcutaneous Devices

With transcutaneous devices such as flexible catheters, the dressing 10is placed on the skin around the catheter 32 by passing the catheter 32through the slit 26. The dressing 10 is rotated, if needed, to ensurethat slit 26 is roughly perpendicular to the long axis of the catheter32, thus ensuring that the portion of the catheter 32 protruding fromthe skin is contacted by the upper surface 40 of the bottom dressing 22.The top dressing 20 is folded over the bottom dressing 22 (or placedover, if the top and bottom dressings are separate), such that the lowersurface 42 of the top dressing 20 is in contact with the portion of thecatheter 32 protruding from the skin. If the anti-microbial material isan anti-microbial metal coating, the dressing is then moistened withdrops of sterile water or 70% ethanol, in order to activate the coatingfor release of anti-microbial metal species. The dressing 10 is thensecured in place with an occlusive or semi-occlusive layer 36, such asan adhesive film, which keeps the dressing in a moist environment.

If the transcutaneous device is rigid, such as a temporary orthopedicpin, the bottom dressing 22 is put in place as set out above, but thetop dressing 20 is then folded and secured around the portion of the pinprotruding from the skin, in a tent-like manner, since the pin generallyprotrudes at an angle normal to the skin surface.

Animal trials with the dressing of the present invention, carrying abi-layer anti-microbial coating formed with silver having atomicdisorder, manufactured as set out above and as described in greaterdetail in Example 3, have shown excellent results in controllinginfection. In use, the dressings are kept moist, at 100% relativehumidity. Adding sterile water initially to activate the anti-microbialmetal coating is needed, and then as needed to maintain the dressing ina moist condition. Dressings may be changed as required for observationand cleaning, but need not be changed more frequently than every 7 days,and can provide an anti-microbial effect for a much longer period oftime.

Multilayer Anti-Microbial Materials With Interference Colour

The dressings preferably include the anti-microbial metal coating formedwith at least two metal layers, a base layer and a top layer over thebase layer, so as to produce an interference colour, as set forth inWO98/41095. Both layers are partly reflective, the top layer is partlylight transmissive. The top layer is a thin film containing at least oneanti-microbial metal formed with sufficient atomic disorder such thatthe top layer, in contact with an alcohol or water based electrolyte,releases ions, atoms, molecules or clusters of the anti-microbial metalat a concentration sufficient to provide a localized anti-microbialeffect on a sustainable basis. In this way, the top layer, in contactwith the alcohol or electrolyte, will undergo a change in optical pathlength, either by a change in thickness resulting from some dissolution,or through a change in the refractive index of the top layer resultingfrom a change in the composition of a newly formed thin layer formed onthe top layer. Either or both of these results are sufficient to cause adetectable colour change, thus providing an indicator that the top layerhas been activated.

Both the base layer and the top layer are formed from a partlyreflective material. In this way, at least a portion of the incominglight is reflected from the surface of the layer while another portionis transmitted through the layer. The top layer is partly lighttransmissive to allow incident light to reach the interface with thebase layer. The top layer thus cannot approximate 100% reflectivity,such as in pure Al or Ag, or interference colours cannot be generated,as is well known in the art. The materials for the top and base layersshould be balanced in their reflectances in order to generate aninterference colour. Generally, the top layer is deposited as a thinfilm having a thickness which maintains adequate transmittance togenerate an interference colour. Furthermore, the refractive index forthe materials in layers is different, accomplished by differences intheir actual or effective compositions. For instance different materialsin the two layers will result in the materials having different actualrefractive indexes. However, if it is desired to make the layers fromthe same material, the layers can be deposited with different porositiesor different levels/types of atomic disorder, in order to achievedifferent effective compositions, and thus different refractive indexes.

In this manner, incoming light reflects off the interface of the baseand top layers. Incoming light reflects from the interface of the toplayer with air, and interferes with the light reflected from theinterface with the base layer so as to generate an “interferencecolour”. The particular colour which is generated and its brightnesswill depend on the properties of the layers, most importantly on thecomposition of the layers, which determines its transmittance andabsorption properties, along with its refractive index, and on thethickness of the layers. Generally, it is desirable to generate firstand second order interference colours, by limiting the thickness of thebase layer and top layers to minimize the number of internalreflections. First and second order interference colours are generallybrighter than third and fourth order etc. colours, making them moreaesthetically pleasing, more consistently reproducible in manufacturing,and more susceptible to detectable colour change on variations inthickness on dissolution of even a minor amount of the top layer.

The property which determines the particular colour which is generatedis the effective optical thickness of the top layer, that is the productof the refractive index of the top layer material and the actualthickness of the top layer. Thus the colour which is desired can bealtered by changing the actual thickness or the top layer or itsrefractive index.

Preferably, the material in the base layer is a reflective metal. Suchmetals are known in the art and include, for example one or more of thevalve metals, e.g., Ta, Nb, Ti, Zr and Hf, as well as transition metalssuch as Au, Ag, Pt, Pd, Sn, Cu, V, W and Mo, or the metal Al. Morepreferably, the base material is formed from Ag, Au, Pt, Pd, Cu, Ta andAl. Use of a metal such as tantalum as the base layer may causereduction of oxide containing materials in the top layer. To avoid this,a barrier layer (not shown), such as tantalum oxide formed by anodizingat least a portion of the top surface of the Ta metal, should beincluded above a tantalum layer. Preferred metals for the base layer arethe anti-microbial metals Au, Ag, Pt, Pd, Sn and Cu, more preferably Au,Pt and Ag, and most preferably Ag, in a partly reflective form.

The base layer may be formed by known techniques, such as the vapourdeposition techniques of evaporation or physical vapour deposition.Preferably, the base layer is formed as a thin film by physical vapourdeposition with atomic disorder, as set out below and in U.S. Pat. No.5,454,889, in order to produce a sustainable anti-microbial effect whenthe base layer is ultimately exposed to an alcohol or water basedelectrolyte. The thickness of the base layer is generally not critical,provided that it is partly reflective. Preferred thicknesses will varywidely with the material composition and the desired colour. However, inthat the layer is preferably a thin film formed by physical vapourdeposition techniques, it should be at least about 25 nm thick to createa useful colour. To generate first and second order interference coloursand to produce an anti-microbial effect, the base layer should begreater than 60 nm thick, more preferably 300 to 2500 nm thick, and mostpreferably 600 to 900 nm thick.

The top layer is formed of a partly reflective, partly lighttransmissive thin film containing at least one anti-microbial metalformed with atomic disorder so as to produce a sustainableanti-microbial effect, and ultimate colour change, when exposed to analcohol or a water based electrolyte. The anti-microbial metal ispreferably one or more of Ag, Au, Pt, Pd, Ir, Sn, Cu, Sb, Bi, and Zn ina partly reflective, partly transmissive form. More preferably, theanti-microbial metal is Ag, Au, Pt, Pd or Cu. The thickness of the toplayer formed from these metals is preferably less than 400 nm in orderto maintain the preferred level of light transmission. The desiredthickness will vary with the composition of the top layer, and with thedesired end colour and colour change. For first and second orderinterference colours, the thickness will generally be less than about400 nm. More preferably, the thickness will range from 5 to 210 nm, mostpreferably from 10 to 100 nm.

The top layer may be a thin film of the base layer material, formed witha different refractive index for instance by altering the depositionconditions to change the porosity, composition and/or degree of atomicdisorder in the layers.

When the base layer is itself formed from an anti-microbial metal withatomic disorder, the top layer may be provided as an in situ generatedtop layer by virtue of its thickness and/or composition changing oncontacting an alcohol or water based electrolyte, so as to produce aninterference colour which differs from the initial colour of the baselayer.

Most preferably, the top layer is a thin film of a composite materialformed by co-, sequentially or reactively depositing an anti-microbialmetal in a matrix with atoms or molecules of a different material tocreate atomic disorder in the matrix, in the manner set out below. Thedifferent material is selected from a) biocompatible metals, b) oxygen,nitrogen, hydrogen, boron, sulphur or halogens, or c) an oxide, nitride,carbide, boride, halide, sulphide or hydride of either or both of ananti-microbial metal or a biocompatible metal. Most preferably, the toplayer material is a composite material containing silver, and one orboth of silver oxide and atoms or molecules containing oxygen trapped orabsorbed in the silver matrix. The term “silver oxide” is meant toinclude any oxide or mixture of oxides of silver. However, the top layeris preferably not formed solely of AgO and/or Ag₂O, since the solubilityof these materials is low for providing a useful anti-microbial effect.

Anti-Microbial Materials Containing Atomic Disorder

At least the top layer, and preferably also the base layer, is formed ina crystalline form from anti-microbial metals with atomic disorder so asto produce an anti-microbial effect. The production of atomic disorderthrough physical vapour deposition techniques is described in U.S. Pat.No. 5,454,886, and as outlined below.

The anti-microbial metal is deposited as a thin metallic film on one ormore surfaces of the dressing 10, by vapour deposition techniques.Physical vapour techniques, which are well known in the art, all depositthe metal from the vapour, generally atom by atom, onto a substratesurface. The techniques include vacuum or are evaporation, sputtering,magnetron sputtering and ion plating. The deposition is conducted in amanner to create atomic disorder in the coating as defined above.Various conditions responsible for producing atomic disorder are useful.These conditions are generally those which one has been taught to avoidin thin film deposition techniques, since the object of most thin filmdepositions is to create a defect free, smooth and dense film (see forexample J. A. Thornton, supra). While such conditions have beeninvestigated in the art, they had not been linked to enhanced solubilityof the coatings so-produced prior to Applicants inventions.

The preferred conditions which are used to create atomic disorder duringthe deposition process include:

a low substrate temperature, that is maintaining the surface to becoated at a temperature such that the ratio of the substrate temperatureto the melting point of the metal (in degrees Kelvin) is less than about0.5, more preferably less than about 0.35 and most preferably less thanabout 0.3; and optionally one or both of:

a higher than normal working (or ambient) gas pressure, i.e. for vacuumevaporation: e-beam or arc evaporation, greater than 0.01 mT, gasscattering evaporation (pressure plating) or reactive arc evaporation,greater than 20 mT; for sputtering: greater than 75 mT: for magnetronsputtering: greater than about 10 mT; and for ion plating: greater thanabout 200 mT; and

maintaining the angle of incidence of the coating flux on the surface tobe coated at less than about 75°, and preferably less than about 30°

The metals used in the coating are those known to release ions etc.having an anti-microbial effect, as set out above. For most dressings,the metal must also be biocompatible. Preferred metals include the noblemetals Ag, Au, Pt, Pd, and Ir as well as Sn, Cu, Sb, Bi, and Zn oralloys or compounds of these metals or other metals. Most preferred isAg or Au, or alloys or compounds of one or more of these metals.

For economic reasons, the thin metal film has a thickness no greaterthan that needed to provide release of metal ions on a sustainable basisover a suitable period of time, and to generate the desired interferencecolour. Within the preferred ranges of thicknesses set out above, thethickness will vary with the particular metal in the coating (whichvaries the solubility and abrasion resistance), and with the degree ofatomic disorder in (and thus the solubility of) the coating. Thethickness will be thin enough that the coating does not interfere withthe dimensional tolerances or flexibility of the device for its intendedutility.

The anti-microbial effect of the material so produced is achieved whenthe coating is brought into contact with an alcohol or a water basedelectrolyte, thus releasing metal ions, atoms, molecules or clusters.The concentration of the metal species which is needed to produce ananti-microbial effect will vary from metal to metal. Generally,anti-microbial effect is achieved in body fluids such as plasma, serumor urine at concentrations less than about 0.5-5 μg/ml.

The ability to achieve release of metal atoms, ions, molecules orclusters on a sustainable basis from a coating is dictated by a numberof factors, including coating characteristics such as composition,structure, solubility and thickness, and the nature of the environmentin which the device is used. As the level of atomic disorder isincreased, the amount of metal species released per unit time increases.For instance, a silver metal film deposited by magnetron sputtering atT/Tm<0.5 and a working gas pressure of about 7 mTorr releasesapproximately ⅓ of the silver ions that a film deposited under similarconditions, but at 30 mTorr. will release over 10 days. Films that arecreated with an intermediate structure (ex. lower pressure, lower angleof incidence etc.) have Ag release values intermediate to these valuesas determined by bioassays. This then provides a method for producingcontrolled release metallic coatings. Slow release coatings are preparedsuch that the degree of disorder is low while fast release coatings areprepared such that the degree of disorder is high.

For continuous, uniform coatings, the time required for totaldissolution will be a function of film thickness and the nature of theenvironment to which they are exposed. The relationship in respect ofthickness is approximately linear, i.e. a two fold increase in filmthickness will result in about a two fold increase in longevity.

It is also possible to control the metal release from a coating byforming a thin film coating with a modulated structure. For instance, acoating deposited by magnetron sputtering such that the working gaspressure was low (ex. 15 mTorr) for 50% of the deposition time and high(ex. 30 mTorr) for the remaining time, has a rapid initial release ofmetal ions, followed by a longer period of slow release. This type ofcoating is extremely effective on devices such as urinary catheters forwhich an initial rapid release is required to achieve immediateanti-microbial concentrations followed by a lower release rate tosustain the concentration of metal ions over a period of weeks.

The substrate temperature used during vapour deposition should not be solow that annealing or recrystallization of the coating takes place asthe coating warms to ambient temperatures or the temperatures at whichit is to be used (ex. body temperature). This allowable ΔT, that thetemperature differential between the substrate temperature duringdeposition and the ultimate temperature of use will vary from metal tometal. For the most preferred metals of Ag and Au, preferred substratetemperatures of −20 to 20° C., more preferably −10° C. to 100° C. areused.

Atomic order may also be achieved, in either or both of the base and toplayers by preparing composite metal materials, that is materials whichcontain one or more anti-microbial metals in a metal matrix whichincludes atoms or molecules different from the anti-microbial metals.

The preferred technique for preparing a composite material is to co- orsequentially deposit the anti-microbial metal(s) with one or more otherinert, biocompatible metals selected from Ta, Ti, Nb, Zn, V, HF, Mo, Si,Al and alloys of these metals or other metal elements, typically othertransition metals. Such inert metals have a different atomic radii fromthat of the anti-microbial metals, which results in atomic disorderduring deposition. Alloys of this kind can also serve to reduce atomicdiffusion and thus stabilize the disordered structure. Thin filmdeposition equipment with multiple targets for the placement of each ofthe anti-microbial and inert metals is preferably utilized. When layersare sequentially deposited the layer(s) of the inert metal(s) should bediscontinuous, for example as islands within the anti-microbial metalmatrix. The final ratio of the anti-microbial metal(s) to inert metal(s)should be greater than about 0.2. The most preferable inert metals areTi, Ta, Zn and Nb. It is also possible to form the anti-microbialcoating from oxides, carbides, nitrides, sulphides, borides, halides orhydrides of one or more of the anti-microbial metals and/or one or moreof the inert metals to achieve the desired atomic disorder.

Another composite material may be formed by reactively co- orsequentially depositing, by physical vapour techniques, a reactedmaterial into the thin film of the anti-microbial metal(s). The reactedmaterial is an oxide, nitride, carbide, boride, sulphide, hydride orhalide of the anti-microbial and/or inert metal, formed in situ byinjecting the appropriate reactants, or gases containing same, (ex. air,oxygen, water, nitrogen, hydrogen, boron, sulphur, halogens) into thedeposition chamber. Atoms or molecules of these gases may also becomeabsorbed or trapped in the metal film to create atomic disorder. Thereactant may be continuously supplied during deposition for codepositionor it may be pulsed to provide for sequential deposition. The finalratio of anti-microbial metal(s) to reaction product should be greaterthan about 0.2. Air, oxygen, nitrogen and hydrogen are particularlypreferred reactants.

The above deposition techniques to prepare composite coatings may beused with or without the conditions of lower substrate temperatures,high working gas pressures and low angles of incidence previouslydiscussed. One or more of these conditions are preferred to retain andenhance the amount of atomic disorder created in the coating.

EXAMPLES Example 1

This example shows the preparation of a bilayer anti-microbial silvercoating on a dressing material. A high density polyethylene dressing,DELNET™ or CONFORMANT 2™ was coated with a silver base layer and asilver/oxide top layer to generate a coloured anti-microbial coatinghaving indicator value. The coating layers were formed by magnetronsputtering under the conditions set out in Table 1. TABLE 1 SputteringConditions: Base Layer Top Layer Target 99.99% Ag 99.99% Ag Target Size20.3 cm diameter 20.3 cm diameter Working Gas 96/4 wt % Ar/O₂ 96/4 wt %Ar/O₂ Working Gas Pressure 40 mTorr 40 mTorr Power 0.3 kW 0.15 kWSubstrate Temperature 20° C. 20° C. Base Pressure 3.0 × 10⁻⁶ Torr 3.0 ×10⁻⁶ Torr Anode/Cathode Distance 100 mm 100 mm Sputtering Time 7.5-9 min1.5 min Voltage 369-373 V 346 V

The resulting coating was blue in appearance. A fingertip touch wassufficient to cause a colour change to yellow. The base layer was about900 nm thick, while the top layer was 100 nm thick.

A zone of inhibition test was conducted. Mueller Hinton agar wasdispensed into Petri dishes. The agar plates were allowed to surface dryprior to being inoculated with a lawn of Staphylococcus aureusATCC#25923. The inoculant was prepared from Bactrol Discs (Difco, M.)Which were reconstituted as per the manufacturer's directions.Immediately after inoculation, the coated materials to be tested wereplaced on the surface of the agar. The dishes were incubated for 24 hr.at 37° C. After this incubation period, the zone of inhibition wascalculated (corrected zone of inhibition=zone of inhibition−diameter ofthe test material in contact with the agar). The results showed acorrected ZOI of about 10 mm.

The coating was analyzed by nitric acid digestion and atomic absorptionanalysis to contain 0.24+/−0.04 mg silver per mg high densitypolyethylene. The coating is a binary alloy of silver (>97%) and oxygenwith negligible contaminants, based on secondary ion mass spectroscopy.The coating, as viewed by SEM, was highly porous and consisted ofequiaxed nanocrystals organized into coarse columnar structures with anaverage grain size of 10 nm. Silver release studies demonstrated thatsilver was released continuously from the coating until an equilibriumconcentration of about 66 mg/L was reached (determined by atomicabsorption), a level that is 50 to 100 times higher than is expectedfrom bulk silver metal (solubility≦1 mg/L).

By varying the coating conditions for the top layer to lengthen thesputtering time to 2 min, 15 sec., a yellow coating was produced. Thetop layer had a thickness of about 140 nm and went through a colourchange to purple with a fingertip touch. Similarly, a purple coating wasproduced by shortening the sputtering time to 1 min, to achieve a toplayer thickness of about 65 nm. A fingertip touch caused a colour changeto yellow.

Example 2

This example is included to demonstrate a multilayer transcutaneousdevice dressing in accordance with the present invention. High densitypolyethylene mesh dressing material DELNET™ or CONFORMANT 2™ dressingwas coated with a bilayer blue anti-microbial coating as set forth inExample 1, using the sputtering conditions of Table 1. Two layers ofthis coated dressing material were placed above and below an absorbentcore material formed from needle punched rayon/polyester (SONTARA™8411). With the silver coating on both the first and third layers, thedressing may be used with either the blue coating side or the silverside in the skin facing position. For indicator value, it might bepreferable to have the blue coating visible. The three layers werelaminated together by ultasonic welding to produce welds between allthree layers spaced at about 2.5 cm intervals across the dressing. Thisallowed the dressing to be cut down to about 2.5 cm size portions forsmaller dressing needs while still providing at least one weld in thedressing portion.

The coated dressings were sterilized using gamma radiation and asterilization dose of 25 kGy. The finished dressing was packaged insealed individually polyester peelable pouches, and has shown a shelflife greater than 1 year in this form. The coated dressings can be cutIn ready to use sizes, such as 5.1×10.2 cm strips, and slits formedtherein before packaging. Alternatively, the dressings may be packagedwith instructions for the clinician to cut the dressing to size and formthe desired length of the slit for the medical device.

Example 3

This animal study evaluated four prototype catheter dressings, one ofwhich was in made in accordance with Example 2 above, the others being 3cm disc shaped catheter dressings of laminated dressing materials,having a thickness less than about 1 mm, formed with a slit to theircenter to fit beneath the catheter, and being coated with a silvercoating deposited as in Example 1. The silver coatings were prepared ina full scale roll coater under conditions to provide coatings having thesame properties set out in Examples 2 and 3 above.

The prototype dressings were as follows:

1. Silver Catheter Dressing, prepared as in Example 2, with a top and abottom dressing sized 5.1×5.1 cm, with a 2.6 cm slit in the bottomdressing, as an example of this invention.

2. Silver Disc 1—A 3 cm disc of the dressing material of Example 2, butused only as a flat disc beneath the catheter (i.e., with no topdressing)

3. Silver Disc 2—A 3 cm disc of the dressing material which included afirst layer of silver coated DELNET, as set out in Example 1, laminatedto STATEX, AET, 8.0NP₂-A/QW, which is a layer of 100% rayon on apolyurethane film, used as a flat disc beneath the catheter (i.e. withno top dressing)

4. Silver Foam Disc 3—A 3 cm disc formed of three layers of silvercoated high density polyethylene prepared as in Example 1, alternatingwith two layers of polyurethane foam, L-00562-6 Medical Foam, availablefrom Rynel Ltd., Bootbay, Me., USA, used as a flat disc beneath thecatheter (i.e., with no top dressing).

Fifteen healthy New Zealand white rabbits weighing 2.6 to 2.9 kg wereused. Segments of polyurethane catheters (Arrow polyurethane indwellingcentral venous catheters, 16 Ga, from Arrow International, Inc.,Reading, Pa., USA, cut to 5 cm long) were implanted subcutaneously inthe back of the rabbits. The rabbits were anesthetized with halothane(University of Calgary, LESARC SOP A6—Life & Environmental SciencesAnimal Resource Centre, Standard Operating Procedures). The dorsalthorax and abdomen were clipped and scrubbed with non-antibiotic soap. Ascalpel was used to make a cut on the skin. A 5 cm long catheter segmentwas then inserted into subcutaneous tissue space perpendicular to thespine. Six catheters were implanted in each rabbit. The catheter siteswere dressed with each of the prototype catheter dressings or controlgauzes, such that the protruding portion of the catheter passed throughthe slit of the disc or dressing. In the case of the dressing of thisinvention, Silver Catheter Dressing, the top layer was placed over thecatheter and pressed down so that the dressing surrounded the segment ofthe catheter protruding from the skin. The catheters were sutured to theskin. Three rabbits were dressed with each type of dressing or controldressing.

Bacterial challenges of each site were made by placing bacterialsuspension-soaked gauzes (10×12.5 cm) on the tops of the dressings. Inthis inoculation technique the gauzes used were larger than the testdressings and were in contact with the heads of the catheters whichprotruded above the dressings, as a result the gauzes provided sourcesof bacteria to the surrounding skin, the catheter dressings and thecatheter heads. Five milliliters of bacterial suspension (Staphylococcusaureus ATCC 25923, grown in TSB (tryptic soy broth) overnight, washedwith PBS (phosphate buffered saline) and re-suspended in PBS,concentration adjusted to 10⁷ CFU/ml (colony forming unit)) wasinoculated at each catheter site. An occlusive tape was then placed overthe dressing to ensure a moist environment inside.

The rabbits were observed for seven days and then euthanized on Day 7.The skin was dissected and the inside portion of catheter was carefullyexposed. Catheter sections (1 cm) were cut from the proximal and distalsites to the skin entrance and collected in tubes containing 2 ml of STS(0.4% sodium thioglycolate, 0.85% sodium chloride and 1% Tween™ 20).Adherent bacteria were recovered from the proximal and distal sites ofthe catheters by sonication and vortexing. The solutions were plated onTSA plates using a drop-plate method and bacterial counts were recorded.

During the whole test period, all dressings or discs remained in place,although some curling and folding occurred on three of the Disc 1 typediscs. The results of the colonization rates and bacteria counts for theproximal and distal sites of the implanted catheters are presented inTable 2, with means of n (shown in parentheses) samples. The numbers inparenthesis following the colonization rates represent numbers ofcolonized/total catheters. TABLE 2 Catheter Colonization Rates andBacterial Recovery from Catheters Bacterial Counts Bacterial CountsDressing Colonization Rate for the Proximal for the Distal Site Type (%)Site (CFU/cm) (CFU/cm) Silver   0 (0/18) 0 0 Catheter Dressing SilverDisc 1 38.8 (7/18) 1.8 × 10³ (n = 7) 5.8 × 10² (n = 9)* Silver Disc 247.1 (8/17) 4.6 × 10³ (n = 8) 3.2 × 10² (n = 6)  Silver Foam 33.3 (6/18)1.4 × 10³ (n = 6) 3.0 × 10² (n = 2)  Disc 3 Control  94.4 (17/18)  7.6 ×10⁴ (n = 17) 4.1 × 10³ (n = 11)*Two distal sites had 50 CFU/cm (only one colony was found in one of theduplicate plates, while the proximal sites of the same catheters had nobacteria). This may have been because of contamination. These two sireswere not included when the colonization rate wascalculated for this group.

The data showed that with gauze coverage, 94.4 % of the catheters werecontaminated with bacterial counts averaging over 10⁴ CFU/cm. Withregard to the Silver Catheter Dressing of this invention, it completelyprevented bacterial colonization. The disc type dressings, Discs 1, 2and 3 reduced catheter contamination rates to 38.8%, 47% and 33.3%,respectively. It is expected that these disc dressing materials wouldreduce catheter contamination to a sufficiently low rate if a topdressing of the same material was used with the discs, in accordancewith the present invention.

All publications mentioned in this specification are indicative of thelevel of skill of those skilled in the art to which this inventionpertains. All publications are herein incorporated by reference to thesame extent as if each individual publication was specifically andindividually indicated to be incorporated by reference.

The terms and expressions in this specification are, unless otherwisespecifically defined herein, used as terms of description and not oflimitation. There is no intention, in using such terms and expressions,of excluding equivalents of the features illustrated and described, itbeing recognized that the scope of the invention is defined and limitedonly by the claims which follow.

1. A transcutaneous device dressing for use with a transcutaneousmedical device which has punctured the skin of a patient and which has aportion of the medical device protruding from the skin, comprising: atop and a bottom dressing, both being formed from a flexible materialand having upper and lower surfaces, the lower surfaces being skinfacing when the dressing in use; the bottom dressing having a slitformed therein extending from one edge inwardly to a termination pointwithin the confines of the bottom dressing; an anti-microbial materialprovided without the use of adhesives at the upper and lower surfaces ofthe bottom dressing, and at least at the lower surface of the topdressing; whereby, in use, the bottom dressing is placed next to theskin, the slit allowing the bottom dressing to surround the puncturesite such that the lower surface of the bottom dressing is in contactwith the skin and the upper surface of the bottom dressing is in contactwith a portion of the medical device protruding from the skin, and thetop dressing is placed above the puncture site such that its lowersurface is in contact with a portion of the medical device protrudingfrom the skin, thereby exposing a portion of the medical deviceprotruding from the skin from above and below to the anti-microbialactivity of the anti-microbial material.
 2. A method of dressing thepuncture site of a transcutaneous medical device to limit infection bymicroorganisms from the surrounding skin and a portion of the medicaldevice that protrudes from the skin of a patient, comprising: providinga transcutaneous device dressing, comprising: a top and a bottomdressing, both being formed from a flexible material and having upperand lower surfaces, the lower surfaces being skin facing when thedressing is in use; the bottom dressing having a slit formed thereinextending from one edge inwardly to a termination point within theconfines of the bottom dressing; and an anti-microbial material providedwithout the use of adhesives at the upper and lower surfaces of thebottom dressing, and at least at the lower surface of the top dressing;sliding the bottom dressing in place next to the skin using the slit toallow the bottom dressing to surround the puncture site at thetermination point such that the lower surface of the bottom dressing isin contact with the skin surrounding the puncture site and the uppersurface of the bottom dressing is in contact with a portion of themedical device protruding from the skin; applying the top dressing abovebottom dressing such that the lower surface of the top dressing is incontact with a portion of the medical device protruding from the skin;depending on the anti-microbial material, applying a water or alcoholbased electrolyte to the dressing to release the anti-microbialmaterial; and fixing the top and bottom dressings to the skin.
 3. Thedressing or method as set forth in claim 1 or 2, wherein: the top andbottom dressings are formed from a unitary dressing and are joinedtogether and divided by a fold line.
 4. The dressing or method as setforth in claim 3, wherein: the anti-microbial material is a coating ofan anti-microbial metal applied to the upper and lower surfaces of thebottom dressing, and at least to the lower surface of the top dressing.5. The dressing or method as set forth in claim 4, wherein the slit isformed from the edge of the bottom dressing which is parallel to thefold line.
 6. The dressing or method as set forth in claim 5, whereinthe top and bottom dressings are formed from multilayered, laminateddressing materials.
 7. The dressing or method as set forth in claim 6,wherein the top and bottom dressings are formed from: a first, skinfacing layer formed of a perforated, non-adherent material; a secondlayer laminated to the first layer, and being formed of an absorbentmaterial; and a third layer laminated to one or both of the first andsecond layers.
 8. The dressing or method as set forth in claim 7,wherein the anti-microbial metal coating is formed on the first and thethird layers.
 9. The dressing or method as set forth in claim 8, whereinthe top and bottom dressings are sized so as to provide coverage of theportion of the medical device protruding from the skin of at least about5 mm.
 10. The dressing or method as set forth in claim 9, wherein theanti-microbial metal coating is a thin film containing at least oneanti-microbial metal, said anti-microbial metal being formed withsufficient atomic disorder such that the thin film, in contact with analcohol or water based electrolyte, releases ions, atoms, molecules orclusters of the anti-microbial metal into the alcohol or water basedelectrolyte at a concentration sufficient to provide a localizedanti-microbial effect on a sustainable basis.
 11. The dressing or methodas set forth in claim 10, wherein the anti-microbial metal coatingcomprises: a base layer of a partly reflective material capable ofgenerating an interference colour when covered with a partly reflective,partly light transmissive top layer; a top layer formed over said baselayer, said top layer being a partly reflective, partly lighttransmissive thin film containing at least one anti-microbial metal andhaving a thickness such that a first or second order interference colouris produced, said top layer having a refractive index different fromthat of the base layer, and anti-microbial metal being formed withsufficient atomic disorder such that the top layer, in contact with analcohol or water based electrolyte, releases ions, atoms, molecules orclusters of the anti-microbial metal into the alcohol or water basedelectrolyte at a concentration sufficient to provide a localizedanti-microbial effect on a sustainable basis.
 12. The dressing or methodas set forth in claim 11, wherein the material in the base layer is ametal selected from the group consisting of Ag, Au, Pt, Pd, Cu, Ta, Aland alloys or compounds of one or more of these metals, in a partlyreflective form, and wherein the anti-microbial metal in the top layeris selected from the group consisting of Ag, Au, Pt, Pd, Ir, Sn, Cu, Sb,Bi, Zn, and alloys or compounds of one or more of these metals.
 13. Thedressing or method as set forth in claim 12, wherein the material in thebase layer and the anti-microbial metal in the top layer is a metalselected from the group consisting of Au, Ag, Pt, Pd, and Cu in a partlyreflective form, and is formed by vapour deposition with sufficientatomic disorder such that the top layer, in contact with an alcohol orwater based electrolyte, releases ions, atoms, molecules or clusters ofthe anti-microbial metal into the alcohol or water based electrolyte ata concentration sufficient to provide a localized anti-microbial effecton a sustainable basis.
 14. The dressing or method of claim 13, whereinthe metal in the base and top layer is Ag, Pt or Au.
 15. The dressing ormethod as set forth in claim 14, wherein the top layer is a thin film ofa composite material formed by co-, sequentially or reactivelydepositing the anti-microbial metal by vapour deposition in a matrixwith atoms or molecules of a different material to create atomicdisorder in the matrix, said different material being selected from thegroup consisting of biocompatible metals, oxygen, nitrogen, hydrogen,boron, sulphur or halogens, or an oxide, nitride, carbide, boride,halide, sulphide or hydride of either or both of an anti-microbial metalor a biocompatible metal.
 16. The dressing or method as set forth inclaim 15, wherein the biocompatible metal is selected from the groupconsisting of Ta, Ti, Nb, V, Hf, Zn, Mo, Si and Al.
 17. The dressing ormethod as set forth in claim 15, wherein the anti-microbial metal issilver and said different material is one or both of silver oxide andatoms or molecules containing oxygen trapped or absorbed in the matrix.18. The dressing or method as set forth in claim 17, wherein the toplayer is less than 400 nm thick, and the base layer is at least 25 nmthick.
 19. The dressing or method as set forth in claim 18, wherein thetop layer is between 5 and 210 nm thick, and the base layer is at least60 nm thick.
 20. The dressing or method as set forth in claim 19,wherein the top layer is about 40-160 nm thick and the base layer is atleast about 300 nm thick.
 21. The dressing or method as set forth inclaim 10 or 20, wherein the first and optional third layers are formedfrom a non-woven, perforated, non-adherent high density polyethylenematerial.
 22. The dressing or method as set forth in claim 21, whereinthe second layer is formed from a non-woven, absorbent rayon/polyestermaterial.
 23. The method as set forth in claim 2, wherein the dressingis fixed in place with an occlusive or semi-occlusive layer whichmaintains the dressing in a moist condition.
 24. The method as set forthin claim 23, wherein the occlusive or semi-occlusive layer is anadhesive film.